Known article-handling machines comprise a filling station fed with empty articles and adapted to output articles filled with the pourable food product.
The filling unit substantially comprises a carousel conveyor rotating about a rotation axis, a tank containing the pourable food product, and a plurality of filling devices supported by the carousel conveyor in a position radially external with respect to the rotation axis of the carousel conveyor.
In greater detail, the carousel is provided with a plurality of support elements for respective articles provided to arrange the mouths of respective articles in a lower position with respect to the respective filling devices and to displace the articles along a circumferential arc trajectory about the above said rotation axis integrally to the respective filling devices.
Each filling device essentially comprises a fixed body connected to the carousel and a valve sliding with respect to the fixed body between an open configuration and a closed configuration.
In greater detail, when it is arranged in the open configuration, the valve defines an opening with the fixed body. The pourable product thereby flows from the tank to a filling mouth of the relative article passing through the opening.
Differently, when the valve is arranged in the closed configuration, it sealingly cooperates with an abutment surface defined by the fixed body, thus preventing the pourable product from flowing from tank towards the mouth of the relative article.
In case of contact filling of carbonated products, the mouth of each article is tight-fluid pressed against the body of the respective filling device. In this way, the carbon dioxide contained in the food product is prevented from escaping from the article in the environment.
Differently, in case of contactless filling of still products, the body of the filling device is arranged at a given distance from the mouth of the article to be filled.
Furthermore, in the case of contact filling with carbonated food products, the filling device is required to carry out a plurality of additional operations on the articles, in addition to the filling with the pourable food product.
In greater detail, the articles undergo a pressurization operation before the filling thereof with the pourable food product. Still more precisely, the empty articles are filled with a pressurized gas, so as to render the pressure inside the articles equal to the pressure of the pourable product, during the filling operation.
Furthermore, due to the fact that the inner volume of each article is in tight-fluid contact with the body of the respective filling device, the latter is required to allow the gas contained in the articles to escape during the filling of the articles.
In order to meet all these needs, filling device s are known, for example from US-A-2001/0045242, which comprises:                a filling chamber defined by the body and fluidly connected to a lower portion of the tank filled with the pourable food product; and        a return duct surrounded by the filling chamber and which opens towards the mouth of the article.        
When the valve is in the closed configuration, the filling chamber is divided in a upper part filled with the pourable product and a lower part which faces the mouth of the article.
Furthermore, the filling device shown in US-A-2001/0045242 comprises:                a fluidic line which extends from an upper portion of the tank filled with a pressurized gas, e.g. carbon dioxide or nitrogen dioxide, to the lower part of the filling chamber of the filling device;        a pressurization chamber, which is interposed along the fluidic line; and        a plurality of control valves, which can be controlled to fluidly connect the pressurization chamber with the lower part of the filling chamber before the filling of the article.        
Furthermore, the control valves can be controlled to fluidly connect the return duct with the pressurization chamber, during the filling of the article.
In case of filling with carbonated products, the valve is kept in the closed configuration while the mouth of the article is in tight-fluid contact with the body of the filling device, and the control valves are controlled to allow the flow of the pressurized gas from the upper part of the tank towards the lower part of the filling device.
In this way, the article is pressurized before the filling thereof.
At this stage, the control valves are controlled to prevent the pressurized gas from flowing towards the filling device, and the valve is set in the open configuration.
Accordingly, the food product flows inside the inner volume of the article while the gas contained in the article flows back in the return duct and in the fluidic line towards the pressurization chamber and the upper part of the tank.
As a result, during the filling of the article, the gas previously contained in the article mixes inside the pressurization chamber and the fluidic line with the gas coming from the tank and that has not yet reached the article.
The gas that returns back along the return duct has been in contact with the article and, therefore, contains a certain amount of impurities. As a result, the gas with some impurities coming from the duct contaminates inside the chamber the “clean” pressurized gas coming from the upper part of the tank.
Accordingly, the pressurized gas which eventually pressurizes the inner volume of the article inevitably contains some impurities.
There is, therefore, the risk of contaminating the article during the pressurization thereof, thus generating the risk of contaminating also the food product with which the article will be subsequently filled.
A need is felt within the industry to reduce as far as possible that risk of contaminating the food product.
Furthermore, the filling device also needs to de pressurize the article, after that the filling thereof with the food product has been completed.
A need is felt within the industry to reduce as far as possible the risk that the gas coming out from the articles contaminates the gas which eventually will be injected in the articles.